1. Field of the Invention
The present invention relates to an information recording and reproducing apparatus using optical discs such as, for example, a CD, a DVD, and a Blu-ray Disc.
2. Description of the Related Art
Information recording and reproducing apparatuses using optical discs are mainly directed to DVDs using red lasers. Also, in recent years, Blu-ray Discs, for example, using blue lasers have achieved densification of recording and reproducing information as compared with DVDs in the past.
Owing to this, an information recording and reproducing apparatus is demanded to be capable of recording and reproducing information on and from optical discs, such as a DVD and a Blu-ray Disc, using two different light sources. Japanese Patent Laid-Open No. 2006-79781 (first related art example, hereafter, referred to as the '781 document) discloses a technique to meet such a demand.
FIG. 4 shows an example shown in the '781 document. An optical pickup 306 includes first and second optical systems. The first optical system includes a first light-emitting element 320, a coupling lens 321, a first reflecting mirror 322, a first diffractive element 323, and a first beam splitter 324. Also, the first optical system includes a first collimator lens 325, a second beam splitter 326, a third beam splitter 327, a first objective lens 316, a cylindrical lens 328, a hologram element 329, a first photodetector 330, and a first monitoring photodetector 331.
The second optical system includes a second light-emitting element 332, a half-wave plate 333, a fourth beam splitter 334, a second diffractive element 335, and a fifth beam splitter 336. Also, the second optical system includes a second reflecting mirror 337, a second collimator lens 338, a raising mirror 339, a second objective lens 317, a multilens 340, a second photodetector 341, a third collimator lens 342, and a second monitoring photodetector 343.
The optical pickup 306 includes a moving base 307, necessary optical components provided on the moving base 307, and an object lens driver 308 arranged on the moving base 307. Bearings 307a and 307b are provided at both end portions of the moving base 307. The bearings 307a and 307b are respectively slidably supported by the guide shafts 304.
Also, a fixed block 310 is fixed to the moving base 307. Rear end portions of support springs 313 are connected to the fixed block 310. A movable block 311 is attached to the fixed block 310. Front end portions of the support springs 313 are connected to the movable block 311.
In the optical pickup 306 having the above-described configuration, when the first light-emitting element 320 emits laser light having a wavelength of about 650 nm, the coupling lens 321 converts an optical magnification of the laser light in a forward path. The laser light is reflected by the first reflecting mirror 322 and is diffracted by the first diffractive element 323, so that the laser light is separated into a chief ray and a marginal ray. The separated laser light passes through the first beam splitter 324, is collimated by the first collimator lens 325, and is incident on the second beam splitter 326, except for a portion of the laser light, passes through the second beam splitter 326, is reflected and raised by the third beam splitter 327, and is emitted on a recording surface of an optical disc by the first objective lens 316.
The laser light emitted on the recording surface of the optical disc is reflected by the recording surface, and is incident on the first beam splitter 324 as returning light through the first objective lens 316, the third beam splitter 327, the second beam splitter 326, and the first collimator lens 325. The laser light is reflected by the first beam splitter 324. The beam shape of the laser light is shaped by the cylindrical lens 328. The shaped laser light is incident on the first photodetector 330 through the hologram element 329. When the returning light is incident on the first photodetector 330, a signal, such as an RF signal, is detected, and recording or reproducing of an information signal is performed.
At this time, the portion of the laser light, emitted from the first light-emitting element 320 and being incident on the second beam splitter 326, is reflected by the second beam splitter 326 and is received by the first monitoring photodetector 331. The laser light to be emitted from the first light-emitting element 320 is controlled to have a substantially constant light intensity.
On the other hand, when the second light-emitting element 332 emits laser light having a wavelength of about 405 nm, the half-wave plate 333 rotates a deflection plane of the laser light. A portion of the laser light is reflected by the fourth beam splitter 334 and is diffracted by the second diffractive element 335, so that the laser light is separated into a chief ray and a marginal ray. The separated laser light is reflected by the fifth beam splitter 336, reflected by the second reflecting mirror 337, collimated by the second collimator lens 338, and incident on the second beam splitter 326. The laser light incident on the second beam splitter 326 is reflected by the second beam splitter 326, passed through the third beam splitter 327, raised by the raising mirror 339, and emitted on a recording surface of an optical disc by the second objective lens 317.
The laser light emitted on the recording surface of the optical disc is reflected by the recording surface, and is incident on the fifth beam splitter 336 as returning light, then through the second objective lens 317, the raising mirror 339, and the third beam splitter 327. The laser light passes through the fifth beam splitter 336. The multilens 340 converts an optical magnification of the laser light and shapes the laser light in a backward path. Then, the laser light is incident on the second photodetector 341. When the returning light is incident on the second photodetector 341, a signal, such as an RF signal, is detected, and recording or reproducing of an information signal is performed.
At this time, the portion of the laser light, emitted from the second light-emitting element 332 and being incident on the fourth beam splitter 334, passes through the fourth beam splitter 334, and is received by the second monitoring photodetector 343 through the third collimator lens 342. The laser light to be emitted from the second light-emitting element 332 is controlled to have a substantially constant light intensity.
With the above-described configuration, the optical systems corresponding to the two light sources are provided.
Meanwhile, regarding the appearance of an information recording and reproducing apparatus, reduction in size of the apparatus is demanded so as to be suitable for a notebook computer, a video camera, and the like. To meet this demand, Japanese Patent Laid-Open No. 2004-133987 (second related art example, hereafter, referred to as the '987 document) discloses a technique of sharing a servo/RF sensor by light sources so as to reduce the number of components.
FIG. 5 shows an example of the '987 document. A first light source 101 emits substantially linearly polarized light having a wavelength λ1. A second light source 102 emits substantially linearly polarized light having a wavelength λ2 (λ1<λ2). The first light source 101 is arranged so that a light beam thereof is incident on a first beam splitter 105 as s-polarized light. The first beam splitter 105 reflects a major portion of the light having the wavelength λ1, which is incident thereon as the s-polarized light. A portion of the light passing through the first beam splitter 105 is incident on a first light source power detector 113, so that the light is converted into current or voltage. Then, the current or voltage is inputted into a power control circuit 117, so that the current or voltage is used as a driving current control signal of the first light source 101. The light reflected by the first beam splitter 105 is substantially collimated by a collimator lens 107, reflected by a mirror 108, passed through a hologram 109, passed through a quarter-wave plate 110, thereby being converted into substantially circularly polarized light, and condensed by a condensing lens 111 onto a first information recording medium 112. Herein, it is assumed that the hologram 109 is a polarizing hologram that does not diffract the light (outgoing light) having the wavelength λ1 from the side of the first light source 101, but diffracts the light (returning light) having the wavelength λ1 from the side of the first information recording medium 112. Accordingly, the light can be guided from the first light source 101 to the first information recording medium 112. While the light reflected by the first information recording medium 112 travels through a backward optical path and reaches the first beam splitter 105, the light is converted into p-polarized light when passing through the quarter-wave plate 110. Thus, almost all of the light passes through the first beam splitter 105, and is incident on a second beam splitter 106.
Almost all of the light having the wavelength λ1 passes through the second beam splitter 106. The light passing through the second beam splitter 106 is incident on a signal detector 116 through an optical element 115. The light incident on the signal detector 116 is used for detection of various signals for focusing, tracking, RF, and the like, by a photodetector that is provided in the signal detector 116.
The second light source 102 is arranged such that the second light source 102 is rotated by an angle φ around an optical axis, so that the second beam splitter 106 contains both components of p-polarized light and s-polarized light. The second beam splitter 106 reflects almost all of the light having the wavelength λ2, which is incident thereon as the s-polarized light, but transmits the light with the component of the p-polarized light. The transmitting light is incident on a second light source power detector 114. The light is converted into current or voltage, and the current or voltage is input to the power control circuit 117, so that the current or voltage is used as a driving current control signal of the second light source 102. The light reflected by the second beam splitter 106 is passed through the first beam splitter 105, substantially collimated by the collimator lens 107, reflected by the mirror 108, passed through the hologram 109, passed through the quarter-wave plate 110, and condensed by the condensing lens 111 onto a second information recording medium 118.
With this configuration, for example, as long as the hologram 109 has wavelength selectivity, the light having the wavelength λ2 does not have to be diffracted. The light from the second light source 102 may be guided to the second information recording medium 118. While the light reflected by the second information recording medium 118 travels through a reversed optical path and reaches the second splitter 106, the component of p-polarized light is generated when the light passes through the quarter-wave plate 110. Thus, the light with the component of p-polarized light passes through the second beam splitter 106 and is incident on the signal detector 116 through the optical element 115. The light incident on the signal detector 116 is used for detection of various signals for focusing, tracking, RF, and the like, by the photodetector in the signal detector 116.
However, the above-described related art examples involve the following problems.
Regarding the example in the '781 document, two photodetectors for each light source, that is, four photodetectors, in total, are necessary. Hence, the number of components is increased. Also, the number of wiring lines is increased due to the increase in the number of photodetectors. An area of a flexible printed circuit (FPC), on which the wiring is arranged, may be increased, and the number of connectors of an electrical substrate to be electrically connected to the FPC may be increased. With these factors, the apparatus may be increased in size.
The example in the '987 document involves problems as described below in detail.
A servo/RF sensor has a photodetecting surface that is typically divided into a plurality of sections for calculating a servo signal. Hence, the photodetecting surface has to be highly accurately positioned with respect to an optical axis of light to be incident on the servo/RF sensor.
When the servo/RF sensor is shared by the light sources, as described according to the example in the '987 document, the following problems may occur.
When the position of the photodetecting surface is adjusted with respect to the optical axis corresponding to the first light source, the photodetecting surface may be misaligned with the optical axis corresponding to the second light source, depending on, for example, assembly accuracy of an optical element corresponding to the second light source, such as a positional shift of the second light source. Hence, the quality of a servo signal of the second light source is deteriorated.
Also, a method is provided in which the photodetecting surface is adjusted with respect to the optical axis corresponding to the first light source, and then, the second light source is moved, so that the position of the photodetecting surface is adjusted with respect to the optical axis of the second light source. With this method, however, the following problem occurs. In general, if an optical axis is misaligned with the center of the intensity distribution of the light beams to be incident on an objective lens, for example, when the objective lens is moved in a radial direction of an optical disc by tracking, or the like, the light intensity is seriously changed, and the signal quality may be deteriorated. Therefore, an adjustment method is used, in which the optical axis is aligned with the center of the intensity distribution of the light beams to be incident on the objective lens, by rotationally adjusting the light source around an axis perpendicular to the optical axis. As described above, however, when the position of the optical axis of light to be incident on the servo/RF sensor and the position of the photodetecting surface are adjusted, by moving the second light source, it is extremely difficult to rotationally adjust the light source. This is because it is necessary to use reflected light of light emitted from the objective lens to adjust the position of the photodetecting surface, whereas it is necessary to monitor the light emitted from the objective lens to observe the intensity distribution. Further, a method is provided in which a flat plate is inserted between parallel light beams, and the flat plate is inclined so as to adjust the center of the intensity distribution. With this method, however, the number of components may be increased.
Also, if the flat plate is inclined in light beams that are not completely parallel light beams, but are slightly divergent or convergent light beams due to a variation in components or other factors, astigmatism is generated, and hence, the signal quality is deteriorated. As described above, with the example from the '987 document, the signal quality may be deteriorated.